Over fifty years after the Charles Manson/Tate-LaBianca murders, the “Helter Skelter” slaughter continues to entice and challenge the American psyche.

With all the books, all the films and TV miniseries about it, with even Quentin Tarantino weighing in with a wish fulfillment fantasy riff on the crimes committed “Once Upon a Time…in Hollywood,” it would seem impossible to find a fresh angle on the subject.

But America’s greatest documentarian, Errol Morris, got Netflix money to find one, and he did — “Motive.”

What if the narrative we’ve been fed, that cult leader Manson was obsessed with starting a race war and found legions of compliant 1960s hippies to buy in to his mad obsession with triggering that and join his “family,” was just spin? What if it was just what the “government wanted you to believe,” perhaps motivated by a coverup? Or a Hollywood prosecutor’s angle to help sell a book?

“Chaos: The Manson Murders” wades into possible CIA CHAOS operation connections and MK-ULTRA” experiments, FBI COINTELPRO motives, probing the role LSD was suspected of playing in “mind control” and Charles Manson’s post-prison, pre-murders metamorphisis into a guru.

It taps into the “establishment” paranoias of the time, the “Manchurian Candidate” thinking, a mysterious CIA Dr. “Jolly” with ties to — wait for it — The Kennedy Assassination.

The film is anchored around interviews with journalist/researcher Tom O’Neill as it is largely based on O’Neill’s book, “Chaos: Charles Manson, the CIA and the Secret History of the Sixties.”

“I know that what we were told,” O’Neill says with certainty, “ISN’T what happened.”

As Morris interrogates O’Neill, samples archival interviews (by the likes of Diane Sawyer, Tom Snyder and Geraldo Rivera) with Manson and others convicted of the murders, we start to wonder, as Morris himself must have, if O’Neill has a point.

We hear from a surviving prosecutor, Stephen Kay, who sounds quite reasonable in remaking the state’s case — that the Beatles were prophets in Manson’s mind, that he preached “Helter Skelter” chaos creation to his “family” at the Spahn Movie Ranch where they were holed up, that his racial paranoia drove his thinking and was absorbed by his minions, who painted “Pig” and “Helter Skelter” on the walls and doors of the crime scenes of their murder spree to make “it look like the Black Panthers” did it.

But hearing that the case’s lead prosecutor, Vincent Bugliosi, had his co-writer Curt Gentry in the courtroom, taking notes for the planned book, “Helter Skelter: The True Story of the Manson Murders,” which they knew they could sell the movie rights to, gives us doubts.

When Morris interviews murderous Family member Bobby Beausoleil by phone in prison, he lends a second voice to debunking the Bugliosi “narrative” this story has been sold by for over 50 years.

The Bugliosi bashing is joined by some odd connections between Manson, his San Francisco parole officer and a supposed CIA-experiment-linked “clinic” there during the ’67 “Summer of Love.”

O’Neill has lots of documentation underscoring his CIA theories, but throws a lot of such coincidences and connections against the wall. And while Morris occasionally catches him equivocating, backing down from The Big Conspiracy, we watch and wonder if the great documentarian has wholly bought in. Is there genuine “pushback” coming?

Is that moment where O’Neill, interviewed in an easy chair sitting in a pool of light, glimpses his dog passing behind him a comment on his “Will this dog hunt?” credibility?

Details pile up as we wait for some shoe to drop — the number of blunders in the murders and their planning by Manson & Co., and by the cops, who didn’t tie three separate blood-writing-on-the-wall killings in the same short period of time together.

We hear Manson’s music, a brooding folk crooner who sounds creepily like the “lost” and found singer Rodriguez, and piece together some (but not all) of the connections he made with the music industry in LA.

And as Morris asks more and more pointed questions off camera and we catch snippets of the classic film “The Manchurian Candidate,” we, like Morris, consider all our options.

Do we believe the now-dead, got-rich-on-the-case Bugliosi and his team? Do we think the FBI and CIA manipulated/trained/turned-loose Manson, or that they contorted the case to fit their “discredit the left/anti-war movement” agenda?

Or do we believe the guy who’s still in prison for murder, who unravels what has been pitched as “random” wanton slaughter as a series of mistaken addresses, misplaced grudges and crimes to cover up other crimes?

How important was “the music” in all of this?

Morris, the master interrogator, keeps his powder dry to let the assorted spokesfolks make their cases, only occasionally allowing the filmmaker’s incredulity into his finished film.

We’re meant to make our own judgement as to who makes the best case. As for me, let’s just say I left this film waiting for Bobby Beausoleil’s book on the subject.

Only Errol Morris could make a murderer in prison come off more credible than pretty much anybody else in a true crime documentary.

Rating: TV-MA, violence

Cast: Tom O’Neill, Charles Manson, Stephen Kay, Vincent Bugliosi, Bobby Beausoleil, Tex Watson, Bernard Crowe, Gregg Jakobson and Errol Morris

Credits: Directed by Errol Morris, based on the book by Tom O’Neill and Dan Piepenbring. A Netflix release.

Running time: 1:39